The gases emitted by internal combustion engines represent the main source of atmospheric pollution and depend directly on the quality of the combustible used. Different actions have been carried out worldwide for the production and refining of higher quality gasoline and diesel. For example, since 2005 the European Union set the upper limit of 50 ppm of sulfur in diesel and gasoline; however Germany has gone further and reduced to 10 ppm. For the United States of America the standard for the maximum content of sulfur in gasoline will be 80 ppm and 30 ppm as average. In Mexico, PEMEX (Pemex Refining), based on their commitment to producing and distributing gasoline to comply with environmental laws and international standards of quality, is adjusting its parameters to produce gasoline, as a rule establishing maximum sulfur content between 15 and 30 ppm from 2008 until 2010.
The most used treatment for desulfurization of gasolines in refining processes is catalytic hydrodesulfurization at high temperature and pressure (HDS process) (I. Pachano, J. Guitian, O. Rodríguez, J. H. Krasuk (Intevep. S.A.) U.S. Pat. No. 4,752,376 (1988), Jr. Hensley, L. Albert, L. M. Quick, (Standard Oil Company) U.S. Pat. No. 4,212,729); however this process is very expensive and drastic conditions of operation are required, employing transition metal-containing catalyst, which lose their activity quickly, especially for heavy Mexican oils with higher content of sulfur, which are very difficult for processing and for sulfur removal.
In some countries new Technologies have been developed for resolving this problem (Zaczepinski, S. Exxon Diesel Oil Deep Desulfurization (DODD) in Handbook of Petroleum Refining Processes, ed. R. A. Meyer, McGraw-Hill, NY, 1996, Cap. 8.7; Ito, E.; Rob, J. A.; Veen, R. V. Catal. Today 2006, 116, 446-460; Brunet, S.; Mey, D.; Pérot, G.; Bouchy, C.; Diehl, F. Appl. Catal. A 2005, 278, 143-172) for example the adsorption of sulfur compounds under solid absorbent, this process is known as IRVAD® (U.S. Pat. No. 5,730,860, dated Mar. 24, 1998) from Black & Veatch Pritchard Inc., the process S Zorb® from Phillips Petroleum (http://www.eia.doe.gov/oiaf/servicerpt/ulsd/uls.html) and the process from Haldor Topsoe (EP 1057879, published date: Dec. 6, 2000); the liquid-liquid extractions with common organic solvents (Petrostar Refining, 217 National Meeting, American Chemical Society, Anaheim, Calif., March 1999) oxidative desulfurization with different oxidant agents (Unipure Corp., NPRA Meeting No AM-01-10, March 2001; Sulphco Corp, NPRA Meeting No AM-01-55, March 2001; BP Chemicals UK, Journal of Molecular Catalysis A: Chemical (1997) 397-403; UOP LLC, U.S. Pat. No. 6,171,478 dated Jan. 9, 2001; EXXON Research and Engineering Co., U.S. Pat. No. 5,910,440 dated Jun. 8, 1999, U.S. Patent Publication No. 2002/35306A1 dated Mar. 21, 2002; Fuel 2003, 82, 4015; Green Chem. 2003, 5, 639).
Ionic liquids have attracted the attention of research due to their physicochemical properties, such as: very low vapor pressure, non-flammability, non-corrosives, low toxicity and by these reason they are excellent substitutes of common volatile organic solvents (Wasserscheid, P.; Keim, W. (Eds.) Ionic Liquids in Synthesis, Wiley-VCH, Wenheim, 2004; Welton, T. Chem. Rev. 1999, 99, 2071-2084; Zhao, H.; Malhotra, S. V. Aldrichimica Acta 2002, 35, 75-83) and promote their application in different oil refining processes and for chemical industry (Rogers, R. D.; Seddon, K. R (Eds.) Ionic Liquids: Industrial Applications of Green Chemistry. ACS, Boston, 2002; Rogers, R. D.; Seddon, K. R (Eds.) Ionic Liquids as Green Solvent: Progress and Prospects. (ACS Symposium Series), Boston, 2003; Rogers, R. D.; Seddon, K. R (Eds.) Ionic Liquids IIIB: Fundamentals, Progress, Challenges, and Opportunities: Transformations and Processes (ACS Symposium Series), Boston, 2005; Roger, R. D.; Seddon, K. R.; Volkov, S (Eds.). Green Industrial Applications of Ionic Liquids. (NATO Science Series), Kluwer Academic Publishers, Dordrecht, Netherlands, 2002).
One of the first publications that mention the use of ionic liquid for removing mercaptans from hydrocarbon fluid is WO Publication No. 0234863 with publication date May 2, 2002. The methods described are based on the use of sodium hydroxide in combination of ionic liquids to favor the conversion of mercaptans in mercaptides, which are removed with ionic liquids. During the 2005-2009 years, Peter Wassercheid and coworkers have published several patents and papers about the ionic liquids for the process of the deep desulfurization of hydrocarbons (Chem. Corn. (2001) 2494; WO 03037835 published May 8, 2003, U.S. Patent Publication No. 2005/0010076A1, published Jan. 13, 2005). In these works the author employed ionic liquids with general formula C+A− where C+ is 1,3-dialkyllimidazolium or tetraalkylamonium and A− are tetrachloroaluminates or methanesulfonates. By means of a process with several and successive extractions (up to 8 extractions), high sulfur extraction efficiencies were achieved using model gasolines. However, the use of ionic liquids containing aluminum salts have the problem of the high acidity of chloroaluminates which leads to secondary reactions such as olefins polymerization, in addition ionic liquids containing this anion type are highly hygroscopic and non-stables to atmospheric humidity.
U.S. Patent Publication No. 2003/0085156A1, published May 8, 2003, also makes mention of the use of ionic liquids where the quaternary ammonium or alkylphosphonium are the cations and tetrachloroaluminate as anion. For the extraction of sulfur compounds in synthetic fuels, it is mentioned that these compounds can be oxidized to sulfoxides or sulfones before or during the extraction process.
It was published in Energy & Fuels 18 (2004) 1862, that CuCl-based ionic liquids exhibited desulfurization ability of gasoline when used in an extraction process; as well as a published paper (Zhang, S.; Zhang, Q.; Conrad Zhang, Z. Ind. Eng. Chem. Res. 43 (2004) 614) some ionic liquids properties and sulfur and nitrogen compounds removal from transportation fuels were studied.
In U.S. Patent Publication No. 2004/0045874A1, published Mar. 11, 2004, a process for desulfurization and denitrogenation of hydrocarbon fractions using a wide family of ionic liquids was explored with alkylating agents of high efficiencies.